In many fields it is necessary to blend additives with a main base product to form a desired finished product. Typically, such additives need to be added to the main base product in precise ratios to obtain the required properties in the finished product. Blending additives at ratios other than a specified ratio is undesired, both because the finished product may not perform to specifications and because many additives are relatively expensive and it is uneconomic to waste additive by exceeding the required ratios.
Non-limiting examples of products which undergo additive blending include: gasoline and jet fuels; lubricants; paints; various food products; fertilizers; and pesticides.
Systems for controlling the blending of additives with a base product at required ratios are known. Such systems typically employ a flow meter which outputs a signal every time a pre-defined amount of main product has passed through the flow meter. In response to that signal, a pre-defined amount of an additive is blended into the main product.
Several different types of blending systems are known, perhaps the most common type employing additive injectors which are piston injectors. These systems inject a pre-determined amount of an additive on each stroke of the piston. In response to a signal from a main product flow meter, the piston injector is stroked to inject a predefined amount of additive.
Another type of blending system is the block valve blending system. In this system a solenoid operated on-off, or block, valve is connected to a pressurized supply of additive. An additive flow meter is connected between the block valve and the main product line and, in response to an `inject` signal from a flow meter in the main product line, the block valve is opened by a controller, allowing additive to flow through the additive line flow meter and into the main product line. The controller receives signals from the flow meter in the additive line and, when a signal corresponding to a predefined desired amount of additive is received, the controller closes the block valve. Each time the controller receives the inject signal from the flow meter in the main product line the process is repeated.
Yet another type of blending system is injector streaming. In streaming systems, a controller monitors the main product line to determine the rate of flow, i.e. number of gallons per minute, etc. A second flow meter in the additive line allows the controller to determine the flow rate of the additive. The controller operates a variable position valve to adjust the flow of additive into the main product line. For example, if the desired ratio of additive to main product was 10 ounces of additive per each five gallons of main product and the main product is flowing at 40 gallons per minute, the controller opens the variable additive valve until the additive line flow meter outputs a signal indicating a flow rate of 80 ounces of additive per minute.
Controllers for each of the above-mentioned techniques are known and range from hard-wired systems, wherein for example the main product flow meter produces a pulse which directly triggers a piston injector, to more sophisticated systems such as that shown in U.S. Pat. No. 5,118,008 to Williams.
The Williams reference shows a microprocessor based controller which receives signals from a main product flow meter and operates a block valve to supply additive accordingly. The controller counts the pulses received from the additive flow meter and compares the count to a pre-defined value in its memory. When the count equals the pre-defined value, the controller completes the injection cycle by shutting the additive valve.
However, problems and/or disadvantages exist with the prior art systems. Such systems typically are only able to control a single type of injector, such as block injectors or piston injectors. Also, the prior art systems cannot control more than a single additive injection. When blending a product which includes several additives, either multiple controllers are required to be employed, one for each additive, or the product must be blended in several product runs, one run for each additive required. Further, such systems typically require a manual re-configuration of the system for each finished product to be blended, with the ratio of additive to main product being manually adjusted either physically, by changing the flow meters, or electrically by replacing the pre-defined values stored in the controller.
Perhaps even more disadvantageous is the fact that only the most limited error-checking and/or reporting capabilities are provided in the prior art systems. The lack of error checking and reporting capabilities is increasingly becoming of concern, both to meet regulatory requirements and to ensure that products are correctly and economically produced.